From U.S. Pat. No. 4,617,683 it is known to apply a zipper strip provided with adjacent male and female parts, over the full width of a web of bag material, by engaging a leading area with a vacuum head and moving the head transverse over the upper side of the web to the other edge. Subsequently the zipper strip is welded to the web by means of a thermal seal rod extending from above and an anvil. Alternatively the zipper strip may be provided with a heat activated glue.
From U.S. Pat. No. 4,878,987 it is known to supply the cooperating male and female parts of the zipper strip from both sides, transverse to the web, by means of pusher rolls. The male and female strips are then each pushed from their side towards the centre, guided by transverse ducts, and then welded to the web.
From the international patent application WO 98/03328 it is known to place a zipper strip transverse to the web of bag material by means of a vacuum band positioned above the web and weld the strip to the bag material.
Applying the zipper strips requires a high control of the orientation and the exact location of the strips, as imperfections in it may hinder the further process and may result in malfunctioning.